| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Ian Barwick <barwick(at)gmail(dot)com> |
| Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: 8.4b1: Query returning results in different order to 8.3 |
| Date: | 2009-04-18 17:11:06 |
| Message-ID: | 49EA09AA.2040900@enterprisedb.com |
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| Lists: | pgsql-hackers |
Ian Barwick wrote:
> Note I'm not sure whether this is a bug, or whether the assumption
> made for the original query (that the row order returned by the
> subquery would be carried over to the main part of the query) is
> incorrect but just happened to work as expected pre-8.4.
The latter. Without an ORDER BY (at the outermost level), the order of
the result is not well defined. Before 8.4, UNION was always performed
by a Sort + Unique, which explains why the output is always sorted in
previous releases. 8.4 knows how to perform it with a Hash Aggregate,
which doesn't yield sorted output. You can look at the EXPLAIN output to
see the difference.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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